1. Field of the Invention
The present invention relates to a water-jacket structure for a water-cooled internal combustion engine and, more specifically, to a water-jacket structure for a cylinder block.
2. Description of the Related Art
In an in-line multicylinder water-cooled internal combustion engine disclosed in, for example, Japanese Patent Application Publication No. 2006-105019, cooling water flows through a cooling water inlet formed in one of opposite ends of a cylinder block with respect to a direction in which cylinder bores are arranged, into a cylinder block water jacket surrounding the cylinder bores, and flows through the cylinder block water jacket to cool the cylinder block. Then, the cooling water flows upward through a connecting port formed in an upper part of the other end of the cylinder block into a cylinder head water jacket surrounding combustion chambers, and flows through the cylinder head water jacket to cool the cylinder head.
In a water-cooled internal combustion engine disclosed in Japanese Patent Application Publication No. 2002-13440, a spacer is placed in a cooling water outlet passage connecting to a cooling water outlet of a cylinder block water jacket to improve cooling efficiency by preventing the stagnation of the cooling water.
In the cylinder block water jacket of the water-cooled internal combustion engine disclosed in Japanese Patent Application Publication No. 2006-105019, the cooling water that has flowed into the cylinder block water jacket through the one end of the cylinder block flows in branch flows along side parts, on the opposite sides of the in-line cylinder bores, of the cylinder block water jacket, the branch flows of the cooling water meet at the opposite end of the cylinder block, and then the cooling water flows upward through the connecting port in the upper part of the other end of the cylinder block into the cylinder head water jacket.
The branch flows of the cooling water meet at the other end of the cylinder block water jacket, and the combined water flow leaves the cylinder block water jacket upward. The cooling water that has flowed through an upper part of the cylinder block water jacket also forms a combined upper flow. The cooling water that has flowed through a lower part of the cylinder block water jacket is obstructed by the combined upper flow and cannot smoothly flow upward and stagnates. Consequently, cooling efficiency drops.
In the water-cooled internal combustion engine disclosed in Japanese Patent Application Publication No. 2002-13440, the spacer is placed in the cylinder block water jacket to form a dam that guides the branch flows of the cooling water that has flowed through the side parts of the cylinder block water jacket so that the branch flows may not meet and may smoothly flow upward.
However, the spacer reduces the volume of a space in which the cooling water flows and hence cooling ability is lessened.
The present invention has been made in view of such problems and it is therefore an object of the present invention to provide a water-jacket structure for a water-cooled internal combustion engine, which does not use any member corresponding to the spacer and is capable of improving the cooling ability of the cooling system of the water-cooled internal combustion engine.